Clonal ordering of 17p and 5q allelic losses in Barrett dysplasia and adenocarcinoma

Mutations in beta-catenin and APC genes are uncommon in esophageal and esophagogastric junction adenocarcinomas

Beta-catenin plays important roles in both intercellular adhesion and signal transduction. Mutations in the beta-catenin or adenomatous polyposis coli (APC) gene can alter the degradation of beta-catenin and cause aberrant accumulation of beta-catenin result in increased transcription of target genes. The dysregulated APC/beta-catenin pathway has been recently discovered as an important mechanism of tumorigenesis in various cancers, but its role in esophageal adenocarcinomas is not clear. Therefore, we studied the beta-catenin gene mutation, allelic loss of chromosome 5q, and APC gene mutation in esophageal and esophagogastric junction adenocarcinomas. Two (2%) somatic mutations in exon 3 of the beta-catenin gene, encompassing the region for glycogen synthase kinase-3beta phosphorylation, were detected from 109 adenocarcinomas. Chromosomal allelic loss on 5q was frequent in 45.3% (44/97) of tumors. Only one missense mutation in the mutation cluster region of the APC gene was detected from 38 esophageal and esophagogastric junction adenocarcinomas with the 5q allelic loss. Our results based on partial screening mutational analyses indicate that mutations of APC/beta-catenin pathway, unlike in colorectal carcinoma, involve only a small subset of esophageal and esophagogastric junction adenocarcinoma.

Malignant progression in Barrett's esophagus: pathology and molecular biology

Due to its increasing incidence, esophageal adenocarcinoma and its precursor lesions have received increasing attention in recent years. The histopathologic steps in the process of malignant progression in Barrett's esophagus are well described and include the following: (a) metaplasia of the normal esophageal squamous epithelium to a specialized intestinal glandular epithelium, (b) development of dysplasia (classified histologically as low and high grade), and (c) development of adenocarcinoma characterized by invasive and metastatic potential. Intestinal metaplasia can be identified by the presence of goblet cells, the detection of which can be aided by finding mucin stained by Alcian blue at low pH. Despite this well-characterized sequence, the timing of the development of dysplasia and the subsequent transition to carcinoma and the risk of development of carcinoma in low- and high-grade dysplasia are not precisely known. In addition, there are problems in the identification of dysplasia, including sampling error and interobserver discrepancies among pathologists. A better understanding of the mechanisms of these events would allow early identification and elimination of high-risk lesions before adenocarcinoma with its attendant poor prognosis were able to develop. In order to better understand this process and to potentially identify early markers of malignant transformation, a variety of molecular studies have been carried out in recent years on adenocarcinoma and its precursor lesions in Barrett's esophagus. On the phenotypic level, increased expression and changes in pattern of expression of proliferation marker (Mib-1) Ki-67 antigen, overexpression of p53 protein, overexpression of growth factors such as epidermal growth factor (EGF), c-erbB2, and transforming growth factor (TGF)-a, decreased and abnormal expression of the cell adhesion molecule E-cadherin, and, in carcinomas, increased expression of serine proteases have all been described. A new area of interest is the family of rab proteins, which play an important role in maintaining cell polarity in the gastrointestinal tract. Increased expression of one of these proteins, rab11, has been described in low-grade, but not high-grade dysplasia. In cytogenetic studies, an increased S-phase fraction, followed by an increased tetraploid (4N) fraction and then aneuploidy, has been described. So far, the specific genes which have been most thoroughly investigated have been p53, APC, p16, and the sites of probable tumor suppressor genes, including 3p (FHIT), 13q, and 18q. With only a few exceptions (i.e., rab11 expression, and possibly mutations of FHIT), the numerous molecular abnormalities which have been described occur late in malignant progression, which means that the best marker which presently exists to identify high-risk lesions in Barrett's esophagus is the histologic identification of dysplasia in endoscopic biopsies, especially high-grade dysplasia. We are presently beginning studies using laser microdissection and competitive genomic hybridization (CGH), which could help to identify new chromosomal areas that might contain genes that are crucial in the early phases of malignant progression in Barrett's esophagus. In the future, identification of such early molecular events which predispose to carcinoma development will allow more precise and earlier risk assessment for individual patients, therefore, enabling more effective therapy.

Clinical significance of p53 mutations in adenocarcinoma of the esophagus and cardia

OBJECTIVE

To compare the frequency and spectrum of p53 gene mutations in adenocarcinomas of the esophagus and cardia and to compare clinical and pathologic features in patients with p53 mutant and nonmutant cancers.

SUMMARY BACKGROUND DATA

The p53 gene is commonly mutated in human cancers, and a p53 mutation is reported to be present in more than 50% of esophageal adenocarcinomas. Although many studies have investigated the frequency of p53 protein overexpression in adenocarcinomas of the esophagus or esophagogastric junction, few studies have assessed the frequency and clinical significance of p53 mutations in these tumors. In particular, the prognostic importance of p53 mutation is uncertain. Adenocarcinomas of the esophagus and cardia share many epidemiologic and pathologic features, but it is controversial whether they represent the same tumor. A comparison of the frequency and spectrum of mutations in adenocarcinomas of the esophagus and cardia would test whether these tumors are also similar at the molecular level.

METHODS

DNA was isolated from microdissected paraffin-embedded tumor tissues of patients who underwent esophagogastrectomy for adenocarcinoma of the esophagus (n = 19), cardia (esophagogastric junction, n = 12), or subcardia (n = 6). Exons 5 to 8 of the p53 gene were analyzed for the presence of mutations using the polymerase chain reaction with single-strand conformation polymorphism and DNA sequencing of bands showing abnormal mobility. The presence of mutation was confirmed by selective hybridization of a mutant-specific oligonucleotide to DNA isolated from the tumor.

RESULTS

p53 mutations were identified in 18 of 37 (48.6%) tumors. Patients with p53 mutant tumors were significantly younger and had a significantly poorer prognosis. There was a similar prevalence of p53 mutations in adenocarcinomas of the esophagus (53%) and cardia (58%). In contrast, mutations were relatively uncommon in subcardia adenocarcinomas (one mutant tumor [17%]). The types of mutations found in the esophageal and the cardia cancers were also similar.

CONCLUSIONS

Adenocarcinomas of the esophagus and cardia have a similar frequency and spectrum of p53 gene mutations, suggesting that these tumors have a common pathogenesis. Patients with mutations are younger, have signs of more advanced disease, and have a poorer prognosis than patients without mutations.

Strategies for molecular intervention in esophageal cancers and their precursor lesions

Molecular analysis of malignant transformation in Barrett's epithelium provides insight into the temporal nature and significance of individual genetic events during multistep esophageal carcinogenesis. Potential targets for intervention in esophageal neoplasms include mutations involving retinoblastoma (Rb) and p53 tumor-suppressor pathways as well as tyrosine kinase cascades, which are known to promote cell cycle progression. Data from recent experiments provide the preclinical rationale for novel pharmacologic interventions in established esophageal cancers, and suggest strategies for chemoprevention in patients at risk for the development of these neoplasms.

Clonal expansion and loss of heterozygosity at chromosomes 9p and 17p in premalignant esophageal (Barrett's) tissue

BACKGROUND

Abnormalities involving the p16 (also known as cyclin-dependent kinase N2 [CDKN2], p16 [INK4a], or MTS1) and p53 (also known as TP53) tumor suppressor genes are highly prevalent in esophageal adenocarcinomas. Loss of heterozygosity (LOH) at 9p21 and 17p13 chromosomes (locations for p16 and p53 genes, respectively) is frequently observed in the premalignant condition, Barrett's esophagus. We studied extensively the distribution and heterogeneity of LOH at 9p and 17p chromosomes throughout the Barrett's segment in patients who have not yet developed esophageal adenocarcinoma.

METHODS

We evaluated 404 samples from 61 consecutive patients enrolled in the Seattle Barrett's Esophagus Study from February 1995 through September 1998. All patients had high-grade dysplasia but no diagnosis of cancer. The samples were assayed for LOH at 9p and 17p chromosomes after amplification of genomic DNA by use of polymerase chain reaction and DNA genotyping. The cell fractions were purified by flow cytometry on the basis of DNA content and proliferation-associated antigen labeling. Association between LOH at 9p and LOH at 17p with flow cytometric abnormalities was determined by chi-squared test, and logistic regression models were used to model and test for the extent to which a particular genotype was found in 2-cm intervals.

RESULTS AND CONCLUSIONS

LOH at 9p and 17p chromosomes are highly prevalent somatic genetic lesions in premalignant Barrett's tissue. LOH at 9p is more common than LOH at 17p in diploid samples and can be detected over greater regions of Barrett's epithelium. In most patients with high-grade dysplasia, the Barrett's mucosa contains a mosaic of clones and subclones with different patterns of LOH. Some clones had expanded to involve extensive regions of Barrett's epithelium. LOH at 9p and 17p chromosomes may be useful biomarkers to stratify patients' risk of progression to esophageal cancer.

Barrett's esophagus. Reducing the risk of progression to adenocarcinoma

Barrett's metaplasia develops in 6% to 14% of individuals with gastroesophageal reflux. Barrett's adenocarcinomas are increasing in epidemic proportions for, as yet unknown, reasons; approximately 0.5% to 1% of patients with Barrett's metaplasia develop adenocarcinoma. Heartburn duration and frequency (but not severity), male gender, and white race are major risk factors for developing cancer. Obesity and smoking are weak risk factors. Survival is determined by depth of tumor invasion (stage). Once invasion of the muscularis propria occurs, most patients have developed widespread metastasis, even when clinical staging studies are negative. No currently available therapy results in prolonged survival once metastases develop. Thus, the more widespread use of effective surveillance strategies is the only currently available means for reducing the morbidity and mortality associated with Barrett's adenocarcinoma.

Loss of p53 in F-MuLV induced-erythroleukemias accelerates the acquisition of mutational events that confers immortality and growth factor independence

Erythroleukemias induced by Friend Murine Leukemia Virus (F-MuLV) involve the insertional activation of the proto-oncogene Fli-1, and the inactivation of the p53 tumor suppressor gene. While the activation of Fli-1 is an early, primary transforming event, p53 mutations are correlated with the immortalization of erythroleukemic cells in culture. In this study we have further analysed the role of p53 loss in F-MuLV induced erythroleukemias by examining the progression of this disease in p53 deficient mice. We found that p53-/- mice succumb to the disease more rapidly than p53+/+ littermates. Additionally, of the 112 tumors generated, 19 gave rise to immortal cell lines, eight of which were derived from p53-/- mice, and ten of which were from p53+/- mice. The ability of these primary tumor cells to grow in culture was associated with the complete loss of wild-type p53 in these cell lines. However, cells from many of the tumors induced in p53-/- hosts did not survive in vitro. These results suggest that the loss of p53 does not directly immortalize tumor cells. Instead, we have evidence to suggest that the loss of p53 promotes the accumulation of mutations that are required for survival in culture and that are capable of accelerating tumor progression in vivo. Indeed, mutations causing expression of the growth factor gene erythropoietin (Epo), were detected in two of seven Epo-independent cell lines from p53 deficient primary erythroleukemias. Moreover, the mechanism of activation of the Epo gene in one of these two Epo-independent cell lines involved genomic rearrangement, that is a hallmark of genetic instability. We propose that, in F-MuLV induced-erythroleukemias, p53 loss may encourage the accumulation of further mutations, subsequently conferring a growth advantage and immortality to the transformed erythroblasts.

Polypoid dysplasia in Barrett's esophagus: a clinicopathologic, immunohistochemical, and molecular study of five cases

Dysplasia in Barrett's esophagus (BE) is a precursor to adenocarcinoma and most commonly occurs as a flat, grossly undetectable lesion. Rarely, dysplasia in BE may grow as a polypoid lesion. Most BE-associated polypoid dysplastic lesions have been referred to as "adenomas" because of their histological similarity to a colonic adenoma. BE-associated polypoid dysplastic lesions have been less well characterized than the flat type. Therefore, our aim was to characterize the clinicopathologic and molecular features of five cases of BE-associated polypoid dysplasia and to review the literature on this entity. The cases were evaluated clinically, histologically, immunostained for MIB-1 and p53, and genotyped for loss of heterozygosity (LOH) at the adenomatous polyposis coli (APC) locus. Mucosal biopsy specimens of five BE patients without dysplasia, and five BE cases with high-grade flat dysplasia, were used as controls. The study patients were all male (average age, 71 years) who presented with symptoms of gastroesophageal reflux disease. Endoscopically, all five cases had a well-defined sessile or pedunculated polypoid lesion ranging from 0.4 to 1.5 cm in size in the mid (n = 1) or distal (n = 4) esophagus and were associated with specialized-type BE (four long segment, one short segment). Histologically, the polyps consisted of intestinalized epithelium with low- and high-grade dysplasia. All five cases contained adenocarcinoma (four within the polyp, one in adjacent BE). All polyps showed increased cell proliferation in the form of surface MiB-1 staining and showed positive p53 staining. Three of three (100%) informative cases showed LOH at the APC locus in the dysplastic epithelium and in areas of adenocarcinoma. All five flat dysplasia controls also showed surface MIB-1 staining and p53 positivity, and three of three informative controls showed LOH for APC. None of the nondysplastic BE controls showed any of these findings. Three patients were treated with esophagectomy and two with polypectomy. All were alive, without metastasis, from 2 months to 6 years later. A literature review of esophageal "adenomas" uncovered 12 cases. Four of these had no clinical or pathological information, two were, in fact, gastric heterotopic lesions, one was composed entirely of intestinal-type epithelium, and five were polypoid dysplastic lesions similar to the cases described here (three male, two female; mean age, 59 years). Four of these five cases were associated with adenocarcinoma in the polyp (two intramucosal, two submucosal). In summary, BE-associated polypoid dysplasia share similar clinical, pathological, and molecular features as flat dysplasia and are often associated with adenocarcinoma. Thus, we agree with other authors who recommend that the term adenoma, which usually carries a benign connotation, be abandoned in favor of a descriptive diagnostic term, such as "BE-associated polypoid dysplasia." BE patients with this lesion should be considered strong candidates for esophageal resection similar to lesions of this kind that occur in inflammatory bowel disease.

Clonal analysis of a case of multifocal oesophageal (Barrett's) adenocarcinoma by comparative genomic hybridization

Oesophageal adenocarcinomas arising in Barrett's epithelium occasionally present as multiple lesions. This could be due to either a multifocal presentation of the same tumour, or different neoplasms arising simultaneously in a dysplastic Barrett's oesophagus ('field cancerization'). This is a report of the genetic analysis of multiple neoplastic sites in a Barrett's oesophagus with an extensive area of dysplasia. In addition, the dysplastic Barrett's epithelium was evaluated. For the genetic screening, comparative genomic hybridization (CGH) allowed evaluation of the whole genome of each specimen. Five cancerous regions were selected and subsequently dissected from paraffin-embedded tissue blocks. The use of archival materials enabled a targeted collection of representative tumour locations. Multiple genetic aberrations were detected by CGH in all cancer sites. Losses on 3p, 4, 7q, 18q, and Y, as well as gains on 8q, 9q, 12p, 13q, 17q, 20p and X, were found in each specimen. In four out of the five lesions, simultaneous losses on 9p, 15q, and 16q, with concomitant gains on 5p, 7q, and 10p, were disclosed by CGH. Adjacent high-grade dysplastic Barrett's mucosa shared the losses on 3p, 4, 7q, 9p, 18, and Y, as well as the gains on 5p, 7q, 13q, 17q, and X, thereby confirming its precursor status. Within this single and rare case of multifocal Barrett's adenocarcinoma, a monoclonal genotype was present. This must have been caused by an extensive outgrowth of a single tumour.

Evolution of neoplastic cell lineages in Barrett oesophagus

It has been hypothesized that neoplastic progression develops as a consequence of an acquired genetic instability and the subsequent evolution of clonal populations with accumulated genetic errors. Accordingly, human cancers and some premalignant lesions contain multiple genetic abnormalities not present in the normal tissues from which the neoplasms arose. Barrett oesophagus (BE) is a premalignant condition which predisposes to oesophageal adenocarcinoma (EA) that can be biopsied prospectively over time because endoscopic surveillance is recommended for early detection of cancer. In addition, oesophagectomy specimens frequently contain the premalignant epithelium from which the cancer arose. Neoplastic progression in BE is associated with alterations in TP53 (also known as p53) and CDKN2A (also known as p16) and non-random losses of heterozygosity (LOH). Aneuploid or increased 4N populations occur in more than 90-95% of EAs, arise in premalignant epithelium and predict progression. We have previously shown in small numbers of patients that disruption of TP53 and CDKN2A typically occurs before aneuploidy and cancer. Here, we determine the evolutionary relationships of non-random LOH, TP53 and CDKN2A mutations, CDKN2A CpG-island methylation and ploidy during neoplastic progression. Diploid cell progenitors with somatic genetic or epigenetic abnormalities in TP53 and CDKN2A were capable of clonal expansion, spreading to large regions of oesophageal mucosa. The subsequent evolution of neoplastic progeny frequently involved bifurcations and LOH at 5q, 13q and 18q that occurred in no obligate order relative to each other, DNA-content aneuploidy or cancer. Our results indicate that clonal evolution is more complex than predicted by linear models.

Role of p53 assessment in management of Barrett's esophagus

The risk of developing gastroesophageal adenocarcinoma is increased in patients with Barrett's esophagus. The management of dysplasia in Barrett's esophagus remains controversial. Understanding of the sequence of events preceding malignancy is essential before screening protocols for early diagnosis and preventive measures can be implemented. The aim of this review is to examine the published data on the role p53 assessment may play in the management of Barrett's esophagus. Relevant papers were identified by an extensive text word search of the Medline database and a review of quoted articles. The p53 abnormality occurs more frequently in highly dysplastic epithelium than in nondysplastic epithelium. However, the retrospective nature of most of the available data could be a significant confounding factor. Our current knowledge suggests that p53 protein overexpression does not seem to predict future progression to cancer or determine disease outcome. The p53 abnormality alone can not be reliably used to predict progression of Barrett's esophagus to cancer. We must await long-term evaluation of patients to determine the percentage of patients with p53 gene abnormality, and nondysplastic Barrett's who will progress to dysplasia or carcinoma. Large randomized controlled long-term follow-up studies are much needed.

Molecular evolution of the metaplasia-dysplasia-adenocarcinoma sequence in the esophagus

The incidence of adenocarcinoma of the esophagus has been increasing in developing countries over the last three decades and probably reflects a genuine increase in the incidence of its recognized precursor lesion, Barrett's metaplasia. Despite advances in multimodality therapy, the prognosis for invasive esophageal adenocarcinoma is poor. An improved understanding of the molecular biology of this disease may allow improved diagnosis, therapy, and prognosis. We focus on recent developments in the molecular and cell biology of Barrett's metaplasia, a heterogeneous lesion affecting the transitional zone of the gastro-esophageal junction whose associated molecular alterations may vary both in nature and temporally. Early premalignant clones produce biological and genetic heterogeneity as seen by multiple p53 mutations, p16 mutations, aneuploidy, and abnormal methylation resulting in stepwise changes in differentiation, proliferation, and apoptosis, allowing disease progression under selective pressure. Abnormalities in expression of growth factors of the epidermal growth factor family and cell adhesion molecules, especially cadherin/catenin complexes, may occur early in invasion. Exploitation of these molecular events may lead to a more appropriate diagnosis and understanding of these lesions in the future.

Multiple target sites of allelic imbalance on chromosome 17 in Barrett's oesophageal cancer

Twelve Barrett's adenocarcinomas have been analysed for the occurrence of allelic imbalance (LOH) on chromosome 17 using 41 microsatellite markers. This study provides evidence for 13 minimal regions of LOH, six on 17p and seven on 17q. Four of these centre in the vicinity of the known tumour suppressor genes (TSGs) TP53 (17p13.1), NFI (17q11.2), BRCA1 (17q21.1), and a putative TSG (17p13.3). The tumours all displayed relatively small regions of LOH (1-10 cM), and in several tumours extensive regions of LOH were detected. One tumour displayed only two very small regions of LOH; 17p11.2 and 17p13.1. The frequency of allelic imbalance has been calculated based on the LOH encompassing only one minimal region, and based on all the LOH observations. By both evaluations the highest LOH frequencies were found for regions II (p53), III (17p13.1 centromeric to p53), IV (17p12), V (17p11.2) and VII (NF1, 17q11.2). Our data supports the existence of multiple TSGs on chromosome 17 and challenges the view that p53 is the sole target of LOH on 17p in Barrett's adenocarcinoma.

Distinct regions of frequent loss of heterozygosity of chromosome 5p and 5q in human esophageal cancer

Loss of heterozygosity (LOH) studies reported thus far suggest that tumor suppressor loci on chromosome 5q are important in esophageal cancer (EC) while little is known about the involvement of chromosome 5p. To investigate the potential existence of tumor suppressor gene(s) on chromosome 5 contributing to the development of EC, we performed LOH studies using a total of 24 polymorphic markers spanning the entire chromosome 5. Seventy primary esophageal cancers were microdissected and allelic deletions were detected by polymerase chain reaction (PCR)-single strand conformation polymorphism or by microsatellite analysis. LOH was observed in at least 1 of the loci in 47 of 70 (67%) esophageal tumors. Initially, 40 tumors [24 squamous cell carcinomas (SCC) and 16 adenocarcinomas (ADC)], each with matched histologically normal esophageal mucosa, were analyzed at 15 marker loci on 5p and 5q. A novel locus, D5S667 on 5p15.2, exhibited the highest frequency of LOH (44%) in these tumors along with another previously reported region of frequent deletion, irf-1 (5q31.1). In a series of 30 additional EC tumors (11 SCC and 19 ADC), a detailed LOH analysis of chromosome 5p15.2 region was conducted using 10 additional polymorphic markers, which mapped the frequently deleted region within 1 cM. Overall, LOH at the D5S667 locus was observed more frequently in SCC than in ADC (62% vs. 23%, p = 0.01). This significant rate of LOH of a distinct region of chromosome 5p implicates the existence of a putative tumor suppressor gene locus involved in EC.

p73, a gene related to p53, is not mutated in esophageal carcinomas

A novel gene, termed p73, encodes a protein with a significant homology to p53 and has been mapped at chromosome 1p36.3, which is a locus of multiple suppressor genes for tumors including neuroblastoma and other cancers. Since the 1p36 locus is reported to be deleted and p53 is frequently mutated in esophageal carcinomas, we examined loss of heterozygosity (LOH) and mutation of the p73 gene in 48 untreated esophageal tumors, as well as mRNA expression in 8 tumors. We screened the P1 genomic library to obtain a P1 clone containing the p73 gene and found a polymorphic short tandem CT repeat site at intron 9. Intragenic sequences for 14 PCR primer sets and a primer pair flanking the repeat were also determined for the analysis of PCR single-strand conformation polymorphism (SSCP) and LOH studies, respectively. Expression of p73 mRNA was detectable but at low levels in all 8 tumor tissues by reverse transcriptase PCR. We did not find any type of mutation other than polymorphisms in the 48 esophageal carcinomas, though aberration of the p53 gene on the PCR-SSCP gels was observed in 15 of 38 (39%) tumors of the same set. In addition, LOH for p73 was found in only 2 of 25 (8%) tumors. These results suggest that, at least in esophageal carcinomas, allelic loss or mutation of p73 may not be a main genetic event for the tumorigenesis as it is with p53.

Clinical models of chemoprevention for the esophagus

Esophageal SCC is a complex disease involving multiple etiologic factors. A number of preventive approaches could be taken to reduce the occurrence of the disease including changes in lifestyle and improved nutrition, for example, the inclusion of higher quantities of fruits and vegetables in the diet. Unfortunately, these primary prevention approaches are not easily implemented and often fall short in achieving marked reductions in disease occurrence. Chemoprevention offers another approach to reducing the risk of esophageal SCC that is likely to be useful, even though the clinical trials to date have not resulted in the identification of agents that produce marked inhibitory effects on the development of the disease. Given esophageal SCC's complex etiology, it would appear that the most effective chemoprevention strategy would be to employ agents that reduce mutational events associated with exposure to esophageal carcinogens in combination with agents that inhibit the progression of epithelial dysplasia to esophageal SCC. The feasibility of addressing carcinogen-induced mutational events is underscored by the fact that many of the suspected esophageal carcinogens are known, and inhibitors of these carcinogens have been identified in animal model systems. In addition, biomarkers to assess the efficacy of anti-initiation agents, such as levels of phase I and II enzyme activities and of carcinogen: DNA adducts, can be measured. The identification of agents that inhibit the progression of dysplastic lesions to esophageal SCC has proven difficult; however, the results of the trial with ATB and retinamide are encouraging. Clearly, it seems important to identify the active chemopreventives in the antitumor-B herbal mixture. Further studies to identify strong inhibitors of tumor progression in the rat model for esophageal SCC are also needed. Biomarkers of cell proliferation (e.g., PCNA, Ki67), cell differentiation (keratins), apoptosis, gene expression (EGFR, cyclin D1, p53), and nuclear/nucleolar morphometry can be used in studies to assess the efficacy of chemopreventives to either reverse esophageal dysplastic lesions or slow their rate of progression. The development of viable approaches toward the chemoprevention. of esophageal SCC is truly an important goal in view of the poor prognosis of this disease.

Genetic alterations in Barrett esophagus and adenocarcinomas of the esophagus and esophagogastric junction region

The incidence of esophageal adenocarcinoma has increased markedly in the past two decades, but the genetic alterations in this cancer and its precursor, Barrett mucosa, have not been characterized extensively. DNA replication errors and allelic losses of chromosomes 17p, 18q, and 5q were studied in 36 resected adenocarcinomas arising in the esophagus and esophagogastric junction, 56 Barrett adenocarcinomas, and 11 dysplasias in Barrett esophagus. The results were compared with clinical and pathological characteristics, including patient survival. Replication error positive cancer was rare (5.4%) in esophageal adenocarcinomas and was not found in Barrett mucosa. There was an increase in the prevalence of chromosomal losses in the Barrett mucosa-columnar dysplasia-adenocarcinoma sequence: 17p loss occurred in 14% of Barrett mucosae, 42% of low-grade dysplasias, 79% of high-grade dysplasias, and 75% of adenocarcinomas, respectively; loss of 18q in 32%, 42%, 73%, and 69%; and loss of 5q in 10%, 21%, 27%, and 46%. Clinical stage was a very strong prognostic factor for survival, and adenocarcinomas with allelic loss of both 17p and 18q had worse survival than cancers with no or one allelic loss (P = 0.002). Our results indicate that accumulation of genetic alterations follows the dysplasia-adenocarcinoma sequence in the esophagus and that losses of 18q and 17p occur earlier than 5q loss. Allelic loss of both 17p and 18q in esophageal adenocarcinoma identifies patients with poor prognosis.

Anti-p53 antibodies in patients with Barrett's esophagus or esophageal carcinoma can predate cancer diagnosis

BACKGROUND & AIMS

We previously discovered anti-p53 antibodies predating a cancer diagnosis in subjects at increased risk for liver, lung, breast, and prostate cancer. Recently, we reported a significant correlation (P < 0.017) between p53 antibodies and p53 mutations in patients with late-stage esophageal carcinoma. Because others have reported p53 mutations and overexpression of p53 protein in Barrett's esophagus, we studied p53 antibodies in plasma of 88 serially endoscoped patients: 36 with Barrett's metaplasia, 23 with esophageal squamous cell carcinoma, 10 with esophageal adenocarcinoma, and 19 with esophagitis or normal esophagus.

METHODS

We used enzyme immunoassay, immunoblotting, and immunoprecipitation assays for p53 antibodies; polymerase chain reaction, denaturant gradient gel electrophoresis, and sequencing for p53 mutations; and immunohistochemistry for p53 protein.

RESULTS

p53 antibodies were detected in 4 patients with Barrett's esophagus, including 1 with dysplasia that later progressed to adenocarcinoma, and in 10 cancer patients (P = 0.002) (8 squamous and 2 adenocarcinoma), 2 of whom (1 squamous, 1 adenocarcinoma) had antibodies before cancer was diagnosed. Other patient groups were too small for informative statistical analysis. Six antibody-positive cancer patients had p53 mutations, whereas 2 patients with cancer and 1 with Barrett's esophagus with antibodies had p53 protein overexpressed in esophageal tissues.

CONCLUSIONS

Patients with Barrett's esophagus and esophageal cancer can develop p53 antibodies that may predate the clinical diagnosis of malignancy.

Diagnostic value of p53 immunohistochemistry in Barrett's esophagus: an endoscopic study

The aim of this study was to establish the diagnostic utility of p53 immunohistochemistry in Barrett's esophagus. Three pathologists reviewed endoscopic biopsy specimens and one surgical specimen derived from 102 subjects in a prospective follow-up series. Dysplasia was graded as negative, indefinite, low grade and high grade. p53 staining was assessed as negative, weak or patchy and strong. Kappa coefficients for interobserver agreement for the three combinations of observer pairs were moderate to substantial (0.48, 0.55 and 0.68) for dysplasia and substantial to near perfect (0.77, 0.82 and 0.89) for p53 immunostaining. In the consensus grading achieved for dysplasia, strong p53 staining was recorded in 0/79 samples that were negative or indefinite for dysplasia, 5/15 (33%) examples of low grade dysplasia and 7/8 (87%) examples of high grade dysplasia. Non-dysplastic p53 positive glands were seen in specimens from two subjects harbouring dysplasia or cancer elsewhere. Two p53 positive specimens were, upon review and discussion, re-assigned from low- to high-grade dysplasia. It is concluded that p53 immunohistochemistry facilitates the interpretation of Barrett's epithelium but need only be employed to confirm a suspected diagnosis of dysplasia and assist with the distinction between low- and high-grade dysplasia.

Comparison of p53 and DNA content abnormalities in adenocarcinoma of the oesophagus and gastric cardia

This study examined the association between 17p allelic loss, p53 gene mutation, p53 protein expression and DNA aneuploidy in a series of adenocarcinomas arising in the oesophagus and gastric cardia. 17p allelic loss was detected in 79% (15 of 19) of oesophageal and in 83% (29 of 35) of gastric adenocarcinomas. p53 mutations were detected in 70% (14 of 20) and 63% (26 of 41) of oesophageal and of gastric adenocarcinomas respectively. Both tumour types were associated with a predominance of base transitions at CpG dinucleotides. In five cases of oesophageal adenocarcinoma, the same mutation was detected both in tumour and in adjacent dysplastic Barrett's epithelium. Diffuse p53 protein expression was detected in 65% (13 of 20) and 59% (24 of 41) of oesophageal and of gastric tumours, respectively, and was associated with the presence of p53 missense mutation (Chi-squared, P < 0.0001). DNA aneuploidy was detected in 80% (16 of 20) of oesophageal and in 70% (28 of 40) of gastric tumours. No association was found between p53 or DNA content abnormalities and tumour stage or histological subtype. In conclusion, this study detected a similar pattern of p53 alterations in adenocarcinoma of the oesophagus and gastric cardia--molecular data consistent with the observation that these tumours demonstrate similar clinical and epidemiological features.

Reduced expression of the cadherin-catenin complex in oesophageal adenocarcinoma correlates with poor prognosis

The E-cadherin-catenin complex is important for cell-cell adhesion of epithelial cells. Impairment of one or more components of this complex is associated with poor differentiation and increased invasiveness of carcinomas. Oesophageal adenocarcinomas causes early metastases, progress rapidly, and consequently have a poor prognosis. By means of immunohistochemistry, the expression of E-cadherin and alpha- and beta-catenin was studied in 65 oesophageal adenocarcinomas and 15 lymph node metastases. Expression of these proteins was evaluated with respect to clinico-pathological parameters and patient survival. Expression of the proteins was strongly correlated. In carcinomas, reduced expression of E-cadherin, alpha-catenin, and beta-catenin was found in 74, 60, and 72 per cent, respectively. Expression of E-cadherin and alpha-catenin correlated significantly with stage and grade of the carcinomas, whereas expression of beta-catenin correlated only with grade. Reduced expression of all three proteins correlated with shorter patient survival. In contrast to grade, E-cadherin and beta-catenin were significant prognosticators for survival, independent of disease stage. We conclude that in oesophageal adenocarcinomas, decreased expression of E-cadherin, alpha-catenin and beta-catenin are related events. Furthermore, expression of at least E-cadherin and beta-catenin is significantly correlated with poor prognosis.

The interactions of APC, E-cadherin and beta-catenin in tumour development and progression

Much progress has been made in identifying genes mutated during the development of colorectal carcinoma. Mutation of the APC gene in particular appears to be fundamental for colorectal tumour initiation. In contrast, loss of expression of E-cadherin appears to be a late event, which may be important in the development of invasion. Recent clarification of the function of APC, however, has shown that it exists in equilibrium with beta-catenin and E-cadherin. This review discusses the function of these molecules, their interactions, and how APC mutations may alter the equilibrium with beta-catenin and E-cadherin. It is argued that these changes cause aberrant architectural development of tissue, which results in loss of growth control. It is this escape from growth control, rather than acquisition of cell-autonomous growth, which results in the initial development of adenomas. The role of the E-cadherin-catenin unit in colorectal tumour invasion is discussed and the evidence is reviewed for the involvement of APC and E-cadherin in tumours arising from non-intestinal epithelia.

The molecular basis for carcinogenesis in metaplastic columnar-lined esophagus

A wide variety of biologic events and mechanisms appear to have roles in the development and progression of Barrett's esophagus-associated neoplastic lesions. Figure 5 is a schematic depiction of these events. This is known as an infernogram (named after Dante's Inferno) (S. Kern, unpublished presentations, 1996). Events at the bottom rings of the inferno are high-frequency mutations; nearer to the top of the inferno are the less common events. The next several years promise many further discoveries of not only high-frequency and low-frequency events, but also their application. Some of the molecular alterations already studied show promise as markers for early cancer detection or prognostication. Eventually, applications of these discoveries should yield new and more effective means of preventing and treating the deadly complications of this troublesome premalignant condition.

Biomarkers for malignancy in the columnar-lined esophagus

The biological mechanisms underlying the progression from normal esophageal squamous mucosa to Barrett's epithelium associated with dysplasia and finally to esophageal adenocarcinoma is becoming increasingly well understood. Histologic determination of Barrett's-associated dysplasia remains of paramount importance; however, genetic and biochemical biomarkers of Barrett's metaplasia and dysplasia will facilitate clinical diagnosis, endoscopic surveillance, and monitoring of new therapeutic interventions as they evolve. This article covers conventional and novel biomarkers in Barrett's esophagus.

Reduced expression of the cadherin-catenin complex in oesophageal adenocarcinoma correlates with poor prognosis

The E-cadherin-catenin complex is important for cell-cell adhesion of epithelial cells. Impairment of one or more components of this complex is associated with poor differentiation and increased invasiveness of carcinomas. Oesophageal adenocarcinomas causes early metastases, progress rapidly, and consequently have a poor prognosis. By means of immunohistochemistry, the expression of E-cadherin and alpha- and beta-catenin was studied in 65 oesophageal adenocarcinomas and 15 lymph node metastases. Expression of these proteins was evaluated with respect to clinico-pathological parameters and patient survival. Expression of the proteins was strongly correlated. In carcinomas, reduced expression of E-cadherin, alpha-catenin, and beta-catenin was found in 74, 60, and 72 per cent, respectively. Expression of E-cadherin and alpha-catenin correlated significantly with stage and grade of the carcinomas, whereas expression of beta-catenin correlated only with grade. Reduced expression of all three proteins correlated with shorter patient survival. In contrast to grade, E-cadherin and beta-catenin were significant prognosticators for survival, independent of disease stage. We conclude that in oesophageal adenocarcinomas, decreased expression of E-cadherin, alpha-catenin and beta-catenin are related events. Furthermore, expression of at least E-cadherin and beta-catenin is significantly correlated with poor prognosis.

Epidemiology and molecular biology of Barrett's adenocarcinoma

In the United States, the incidence of esophageal adenocarcinoma has risen faster than any other malignancy in recent years, and now represents the most common histologic type of esophageal cancer observed in major institutions. The precise etiology of this malignancy, and the epidermiologic variables responsible for its dramatically rising incidence, remains obscure. Elucidation of the molecular biology of malignant transformation in Barrett's esophagus may improve the management of patients with advanced esophageal adenocarcinomas. Furthermore, appreciation of the molecular events associated with esophageal adenocarcinomas. Furthermore, appreciation of the molecular events associated with esophageal adenocarcinogenesis may facilitate early detection of occult carcinomas, and enable therapeutic interventions designed to prevent these otherwise highly lethal neoplasms.

The interactions of APC, E-cadherin and beta-catenin in tumour development and progression

Much progress has been made in identifying genes mutated during the development of colorectal carcinoma. Mutation of the APC gene in particular appears to be fundamental for colorectal tumour initiation. In contrast, loss of expression of E-cadherin appears to be a late event, which may be important in the development of invasion. Recent clarification of the function of APC, however, has shown that it exists in equilibrium with beta-catenin and E-cadherin. This review discusses the function of these molecules, their interactions, and how APC mutations may alter the equilibrium with beta-catenin and E-cadherin. It is argued that these changes cause aberrant architectural development of tissue, which results in loss of growth control. It is this escape from growth control, rather than acquisition of cell-autonomous growth, which results in the initial development of adenomas. The role of the E-cadherin-catenin unit in colorectal tumour invasion is discussed and the evidence is reviewed for the involvement of APC and E-cadherin in tumours arising from non-intestinal epithelia.

Mutation analysis of the p53, APC, and p16 genes in the Barrett's oesophagus, dysplasia, and adenocarcinoma

AIMS

To study the loss of heterozygosity and the presence of mutations at the p53, p16/CDKN2, and APC genes in Barrett's oesophagus, low grade dysplastic oesophageal epithelium, and adenocarcinoma of the oesophagus; to relate the presence of alterations at these genes with the progression from Barrett's oesophagus to adenocarcinoma.

METHODS

DNA was extracted from paraffin blocks containing tissue from Barrett's oesophagus (12 samples), low grade dysplasia (15 cases), and adenocarcinoma (14 cases). Loss of heterozygosity (LOH) at the p53, p16, and APC genes was determined by comparing the autoradiographic patterns of several microsatellite markers between the normal tissue and the malignant tissue counterpart. SSCP was used to determine the presence of mutations at p53 (exons 5 to 8), p16 (exon 2), and APC. Homozygous deletion of the p16 gene was defined through polymerase chain reaction followed by Southern blot.

RESULTS

LOH at the p53, p16, and APC genes was not observed in Barrett's oesophagus without dysplasia, and increased to 90% (p53), 89% (p16), and 60% (APC) in the adenocarcinomas. The p53 gene was mutated in only two adenocarcinomas (codons 175 and 245). In one case a mutation at the APC gene (codon 1297) was found. No patient had mutation at the second exon of p16. However, this gene was homozygously deleted in three of the 12 adenocarcinomas.

CONCLUSIONS

The tumour suppressor genes p53, p16, and APC are often deleted in adenocarcinomas derived from Barrett's oesophagus. Mutations at these genes are also found in the adenocarcinomas, including the homozygous deletion of the p16 gene. However, the absence of genetic alterations in the Barrett's oesophagus and the low grade dysplastic epithelia suggest that mutations at these genes develop later in the progression from Barrett's oesophagus to adenocarcinoma.

p53 protein accumulation and p53 gene mutation in esophageal carcinoma. A molecular and immunohistochemical study with clinicopathologic correlations

BACKGROUND

p53 gene mutation and p53 protein accumulation are common in human cancer. However, their clinical significance is controversial and p53 accumulation may not correlate with gene mutation. The current study investigates the occurrence of p53 alterations in esophageal carcinoma, the correlation between the analyses at the gene and protein level, and their prognostic significance.

METHODS

A series of 74 esophageal carcinomas (46 squamous cell carcinomas, 21 Barrett's adenocarcinomas, and 7 undifferentiated carcinomas) was studied by single strand conformation polymorphism (SSCP) analysis and immunohistochemistry (IHC) to detect p53 mutation and accumulation, respectively.

RESULTS

p53 mutations in exons 5-8 were detected in 53% of the carcinomas whereas p53 accumulation was observed in 57% of cases. Comparing SSCP and IHC, there were 27 discordant cases (38%). Overall, only 20 tumors (27%) did not display p53 mutation and/or p53 accumulation. No associations were found between p53 aberrations and clinicopathologic parameters, including patients age and gender tumor type, stage, and grade. p53 protein accumulation and p53 gene mutation were not related to patient survival by univariate or multivariate analysis in esophageal carcinomas.

CONCLUSIONS

p53 aberrations are very common in esophageal carcinomas. However, p53 gene mutation and p53 protein accumulation have a significant discordance, suggesting that p53 function may be inactivated by mechanisms other than mutation. p53 aberrations do not independently predict prognosis in esophageal tumors.

Barrett's esophagus. The significance of p53 in clinical practice

OBJECTIVE

The authors provide an updated review the molecular biology of the p53 tumor suppressor gene with reference to its role in the malignant degeneration of Barrett's esophagus.

SUMMARY BACKGROUND DATA

Appreciation of the function of the tumor suppressor gene p53 has given new insight into regulation of the cell cycle, and the gene appears to play an important role in many solid tumors. Esophageal adenocarcinoma is increasing in frequency in the western world at an alarming rate and is unique because there is a clear metaplasia (Barrett's mucosa)/ dysplasia/carcinoma sequence. p53 malfunction arises as an early event in this carcinogenic process and has been demonstrated in patients with nondysplastic Barrett's metaplasia. The possible causes of p53 malfunction in this setting are discussed. The most reliable method for the detection of p53 mutations is DNA sequencing. p53 immunohistochemistry appears too insensitive to act as a reliable marker for the presence of a mutation and cannot be used as a reliable marker for the future development of cancer.

CONCLUSIONS

High-grade dysplasia within Barrett's mucosa remains the best clinical predictor of adenocarcinoma. The mutational spectrum observed in these tumors should provide clues to their etiology.

17p (p53) allelic losses, 4N (G2/tetraploid) populations, and progression to aneuploidy in Barrett's esophagus

Increased 4N (G2/tetraploid) cell populations have been postulated to be genetically unstable intermediates in the progression to many cancers, but the mechanism by which they develop and their relationship to instability have been difficult to investigate in humans in vivo. Barrett's esophagus is an excellent model system in which to investigate the order in which genetic and cell cycle abnormalities develop relative to each other during human neoplastic progression. Neoplastic progression in Barrett's esophagus is characterized by inactivation of the p53 gene, the development of increased 4N (G2/tetraploid) cell fractions, and the appearance of aneuploid cell populations. We investigated the hypothesis that patients whose biopsies have increased 4N (G2/tetraploid) cell fractions are predisposed to progression to aneuploidy and determined the relationship between inactivation of p53 and the development of 4N abnormalities in Barrett's epithelium. Our results indicate that increased 4N (G2/tetraploid) populations predict progression to aneuploidy and that the development of 4N abnormalities is interdependent with inactivation of the p53 gene in Barrett's esophagus in vivo.

The rationale for esophagectomy as the optimal therapy for Barrett's esophagus with high-grade dysplasia

OBJECTIVE

The authors determined the incidence of invasive adenocarcinoma after esophagectomy in patients endoscopically diagnosed as having Barrett's esophagus with high-grade dysplasia.

SUMMARY BACKGROUND DATA

Barrett's esophagus is a well-recognized premalignant condition. There is controversy with regard to the optimal treatment of high-grade dysplasia in Barrett's esophagus. Recognizing the morbidity and mortality associated with esophagectomy, some recommend a selective approach, reserving esophagectomy only for evidence of invasive cancer identified through endoscopic surveillance. Other advocate esophagectomy for all suitable operative candidates.

METHODS

The authors reviewed their experience between 1985 and 1995 with 11 patients with high-grade dysplasia arising in Barrett's esophagus diagnosed by endoscopic biopsy and treated by esophagectomy.

RESULTS

All patients were white men ranging in age from 47 to 70 years. Ten patients underwent esophagectomy by the Ivor Lewis technique; one had a transhiatal resection. Eight patients (73%) had invasive adenocarcinoma identified after esophagectomy; two (18%) had positive lymph nodes; one required a prolonged hospital stay for an anastomotic leak; two (18%) temporarily suffered delayed gastric emptying. The authors' review identified 85 additional patients previously reported during the same period. Including the current series, 39 patients (41%) had invasive adenocarcinoma identified in the resected specimen. A preponderance of early, potentially curable carcinomas are characteristically found in these patients.

CONCLUSION

A high incidence of endoscopically undetected invasive carcinoma strongly supports esophagectomy as the preferred approach for suitable operative candidates with high-grade dysplasia in Barrett's esophagus.

Mutations of p53 in Barrett's esophagus and Barrett's cancer: a prospective study of ninety-eight cases

We had previously identified p53 mutations in Barrett's esophagus and therefore began a multiinstitutional study to determine their significance as a marker for malignancy. Ninety-eight patients from four institutions were studied. Forty-eight patients (37 men and 11 women, mean age 56.2 years) had Barrett's esophagus with metaplasia or dysplasia but no evidence of malignancy at a mean follow-up of 2.2 years. Barrett's esophagus was classified as metaplasia with no evidence of dysplasia in 32 patients, as low-grade dysplasia in 13, and as high-grade dysplasia in three. The other 50 patients (46 men and four women, mean age 60.2 years) had adenocarcinoma arising in Barrett's esophagus. Tissues from normal stomach or esophagus, tumor, and Barrett's esophagus were obtained for deoxyribonucleic acid analysis by endoscopic biopsy from patients with Barrett's esophagus or cancer or during operations on some patients with Barrett's cancer. Exons 5 through 9 of the p53 gene were studied for mutations by single-strand conformational polymorphism analysis after polymerase chain reaction amplification. Mutations detected by single-strand conformational polymorphism analysis were confirmed by deoxyribonucleic acid sequencing. None of the tissue samples from patients with Barrett's esophagus alone and no dysplasia or low-grade dysplasia had any p53 mutations, but one of the three patients with high-grade dysplasia and no evidence of invasive malignancy did have a p53 mutation. Of the 50 patients with Barrett's cancer, however, 23 (46%) had p53 mutations in Barrett's epithelium, tumors, or both. Twenty of these patients had p53 mutations in the tumor only (n = 16) or in both tumor and Barrett's epithelium (n = 4), suggesting that the mutation plays a direct role in carcinogenesis. Mutations in Barrett's epithelium were found in one patient in the group without malignancy and in seven patients with cancer (one with no dysplasia, two with low-grade dysplasia, and five with high-grade dysplasia). In three patients with cancer, mutations occurred only in Barrett's epithelium, suggesting that such mutations may also be a marker for genomic instability. Mutations were predominantly found in exons 5, 7, and 8, and transitions from guanine to adenine were the most frequent changes. Mutations of p53 are clearly involved in the pathogenesis of Barrett's cancer for a subset of patients (46%), and the fact that we could detect mutations in premalignant Barrett's epithelium supports the hypothesis that p53 mutations may be a useful marker for patients at increased risk for development of invasive cancer.

The molecular biology of esophageal carcinoma

There have been many new developments in our understanding of esophageal carcinoma biology over the past several years. Information regarding both of the major forms of this disease, adenocarcinoma and squamous cell carcinoma, has accumulated in conjunction with data on precursor conditions such as Barrett's esophagus. Some of the most interesting and promising findings have included aneuploidy (abnormal DNA content), amplification and overexpression of proto-oncogenes, loss of heterozygosity at multiple chromosomal loci, and tumor suppressor gene inactivation. Of particular importance is mutation and deletion involving the tumor suppressor gene p53, but abnormalities in the retinoblastoma, deleted in colon cancer, and adenomatous polyposis coli genes have been described as well. Recently, two important cancer pathways implicated in the genesis of multiple tumor types have also been inculpated in esophageal carcinogenesis: the cyclin kinase inhibitor cascade and the DNA mismatch repair process. Alterations in the p16 and p15 cyclin kinase inhibitors, including point mutation and homozygous deletion, have been reported in primary esophageal tumors and/or tumor-derived cell lines. Microsatellite instability, the hallmark of DNA mismatch repair defects, has been detected in esophageal cancers, particularly those associated with Barrett's metaplasia (where it may represent an early event). Further developments in the field of molecular carcinogenesis of esophageal malignancies promise to yield improvements in the early detection, prognostic categorization, and perhaps eventual gene-based therapy of this deadly disease.

Genotypic analysis of multiple loci in somatic cells by whole genome amplification

To screen multiple loci in small purified samples of diploid and aneuploid cells a PCR-based technique of whole genome amplification was adapted to the study of somatic lesions. DNA samples from different numbers of flow-sorted diploid and aneuploid cells from biopsies were amplified with a degenerate 15mer primer. Aliquots of these reactions were then used in locus-specific reactions using a single round of PCR cycles with individual sets of primers representing polymorphic markers for different regions. As a result, polymorphic markers for different chromosomal regions, including VNTRs and dinucleotide repeats, can be used to perform up to 30 locus-specific PCR assays with a single sample obtained from fewer than 1000 cells.

Microsatellite instability in Japanese esophageal carcinoma

Recent studies have shown that microsatellite instability (MSI) may play an important role in the development of various types of cancer. However, there have been only 2 reports describing MSI in esophageal carcinoma and the clinicopathologic significance of MSI in this malignancy has not yet been clarified. To better elucidate the role of genetic instability in the development of esophageal carcinoma, we investigated the presence of MSI in 32 cases of esophageal cancer using paired samples of fresh frozen tumor and normal tissue by a method based on the polymerase chain reaction. MSI was defined as occurring in tumors which showed altered banding patterns at one or more microsatellite loci. The incidence of MSI in esophageal carcinoma was 6 out of 32 patients. MSI was observed more frequently in cases with small-cell carcinoma (2 out of 2) than in cases with squamous-cell carcinoma (4 out of 29). No cases with adenocarcinoma or Barrett's metaplasia were included in our series. No significant correlations between MSI and other clinicopathologic parameters were observed. The present study suggests that (1) some Japanese esophageal carcinomas certainly correlate with DNA replication error, and (2) MSI may be more frequent in small-cell carcinoma of the esophagus than in squamous-cell carcinoma of the esophagus.

Frequent loss of heterozygosity on chromosome 17 at 17q11.2-q12 in Barrett's adenocarcinoma

Allelic loss on chromosome 17 in 18 Barrett's oesophageal tumours was analysed with 17 polymorphic microsatellite markers. Loss of heterozygosity (LOH) of one or more markers was seen in 72% (13 of 18) tumours on 17p and 56% (10 of 18) on 17q. The highest 17p losses were found at D17S799 (62%, five of eight) and D17S261 (55%, five of nine), while loss at the p53 locus was 31% (5 of 16). The highest loss on 17q was found at the TCF-2 (17q11.2-q12) locus with 66% (8 of 12) LOH. TCF-2 was the only marker lost in two of the tumour samples; furthermore, TCF-2 was lost in four other tumours which retained heterozygosity at the markers on either side of it, D17S261 and D17S740. Six markers were used to assess LOH at 17q11.2-q12, and five of eight of the tumour specimens which had LOH at TCF-2 had no other loss on 17q. No statistically significant correlations were found between loss on 17q or 17p and any clinicopathological parameters. We propose from these data that the 17q11.2-q12 region contains a novel predisposing gene in Barrett's adenocarcinomas and may represent the site of a tumour-suppressor gene.

Genetic instability as a consequence of inappropriate entry into and progression through S-phase

The stability of the mammalian genome depends on the proper function of G1 and G2 cell cycle control mechanisms. Two tumor suppressors, p53 and retinoblastoma (Rb), play key roles in progression from G1 into S-phase. We address the mechanisms by which these proteins mediate a G1 arrest in response to DNA damage and limiting metabolic conditions. Gamma-irradiation induced a prolonged, p53-dependent G1 arrest associated with a long-term increase in the levels of the cdk-inhibitor p21WAFl/Cipl (p21). Microinjection of linear plasmid DNA also caused a G1 arrest. The p53-dependent arrest induced by inhibitors of UMP biosynthesis was reversible and occurred in the absence of detectable DNA damage. Both arrest mechanisms contribute to limiting the formation and propagation of damaged genomes. Cells containing mutant p53 but wild-type Rb do not generate methotrexate (Mtx) resistant variants. However, pre-treatment with DNA damaging agents prior to drug selection resulted in resistant clones containing amplified dihydrofolate reductase (DHFR) genes, suggesting that DNA breakage is a rate limiting step for gene amplification. The Mtx-induced arrest did not occur in cells with non-functional Rb. Rb acts as a negative regulator of the E2F transcription factors, and Rb-deficient primary mouse embryo fibroblasts (MEFs) produced elevated levels of mRNA and protein for key E2F target genes. Failure to prevent entry into S-phase in Rb-/- MEFs exposed to DNA-damaging or nutrient limiting conditions caused apoptosis and correlated with p53 induction. Taken together, these findings indicate a link between p53 and Rb function and suggest that their coordination insures correct entry into S-phase, minimizing the emergence of genetic variants.

P53, cell cycle control and apoptosis: implications for cancer

Cellular proliferation depends on the rates of both cell division and cell death. Tumors frequently have decreased cell death as a primary mode of increased cell proliferation. Genetic changes resulting in loss of programmed cell death (apoptosis) are likely to be critical components of tumorigenesis. Many of the gene products which appear to control apoptotic tendencies are regulators of cell cycle progression; thus, cell cycle control and cell death appear to be tightly linked processes. P53 protein is an example of a gene product which affects both cell cycle progression and apoptosis. The ability of p53 overexpression to induce apoptosis may be a major reason why tumor cells frequently disable p53 during the transformation process. Unfortunately, the same genetic changes which cause loss of apoptosis during tumor development, may also result in tumor cell resistance to anti-neoplastic therapies which kill tumor cells by apoptosis. Elucidation of the genetic and biochemical controls of these cellular responses may provide insights into ways to induce cell death and thus hopefully suggest new targets for improving therapeutic index in the treatment of malignancies.

Cell cycle control and cancer

Multiple genetic changes occur during the evolution of normal cells into cancer cells. This evolution is facilitated in cancer cells by loss of fidelity in the processes that replicate, repair, and segregate the genome. Recent advances in our understanding of the cell cycle reveal how fidelity is normally achieved by the coordinated activity of cyclin-dependent kinases, checkpoint controls, and repair pathways and how this fidelity can be abrogated by specific genetic changes. These insights suggest molecular mechanisms for cellular transformation and may help to identify potential targets for improved cancer therapies.

Overexpression of the p53 tumor suppressor gene product in esophageal and gastric carcinomas

PURPOSE

p53 protein has been reported as frequently overexpressed in esophageal and gastric carcinomas. However, the correlation between p53 protein expression and clinico-pathological features of the tumors is debated in this heterogeneous group of cancers. The aim of this study was to establish the prevalence of p53 protein overexpression in a series of resected esophageal squamous carcinomas (n = 78), adenocarcinomas developed on Barrett's esophagus (n = 20), adenocarcinomas of the cardia (n = 36), and adenocarcinomas of the antrum (n = 30), and to correlate this expression with the clinico-pathological and flow-cytometric characteristics of the tumors.

METHODS

Immunohistochemical staining was performed on frozen sections with a monoclonal antibody directed against wild type and mutated p53 protein (Pab 1801). An adjacent frozen specimen was used for flow cytometric determination of the DNA-ploidy and S phase fraction.

RESULTS

p53 protein nuclear expression was detected in 76% of esophageal squamous carcinomas, in 75% of adenocarcinomas developed in Barretts esophagus, in 56% of adenocarcinomas of the cardia, and in 27% of adenocarcinomas of the antrum. Only the number of positive adenocarcinomas of the antrum was significantly lower when compared to the other three types of tumors (p = 0.001). No significant correlation was observed between p53 protein expression and most of the clinico-pathological and flow-cytometric parameters (sex, age, tobacco smoking, chronic alcohol consumption, size of the tumor, grade of differentiation, depth of infiltration, presence of lymph node metastases, UICC stage, DNA-ploidy, S phase fraction). p53 protein expression was more frequent in Lauren's intestinal adenocarcinomas (67%) when compared to the diffuse type tumors (24%) (p = 0.002).

CONCLUSIONS

Our results confirm that overexpression of p53 protein is a common feature of esophageal and gastric carcinomas. The high prevalence of p53 protein overexpression found in cardiac adenocarcinoma when compared to antral adenocarcinoma reinforces the hypothesis of distinct carcinogenetic mechanisms in these two cancers. In particular the lack of correlation between p53 expression and tumor stage suggests that p53 protein overexpression is an early event in these tumors.

DNA damage triggers a prolonged p53-dependent G1 arrest and long-term induction of Cip1 in normal human fibroblasts

The tumor suppressor p53 is a cell cycle checkpoint protein that contributes to the preservation of genetic stability by mediating either a G1 arrest or apoptosis in response to DNA damage. Recent reports suggest that p53 causes growth arrest through transcriptional activation of the cyclin-dependent kinase (Cdk)-inhibitor Cip1. Here, we characterize the p53-dependent G1 arrest in several normal human diploid fibroblast (NDF) strains and p53-deficient cell lines treated with 0.1-6 Gy gamma radiation. DNA damage and cell cycle progression analyses showed that NDF entered a prolonged arrest state resembling senescence, even at low doses of radiation. This contrasts with the view that p53 ensures genetic stability by inducing a transient arrest to enable repair of DNA damage, as reported for some myeloid leukemia lines. Gamma radiation administered in early to mid-, but not late, G1 induced the arrest, suggesting that the p53 checkpoint is only active in G1 until cells commit to enter S phase at the G1 restriction point. A log-linear plot of the fraction of irradiated G0 cells able to enter S phase as a function of dose is consistent with single-hit kinetics. Cytogenetic analyses combined with radiation dosage data indicate that only one or a small number of unrepaired DNA breaks may be sufficient to cause arrest. The arrest also correlated with long-term elevations of p53 protein, Cip1 mRNA, and Cip1 protein. We propose that p53 helps maintain genetic stability in NDF by mediating a permanent cell cycle arrest through long-term induction of Cip1 when low amounts of unrepaired DNA damage are present in G1 before the restriction point.

p53 expression in Barrett's oesophagus, dysplasia, and adenocarcinoma using antibody DO-7

Barrett's oesophagus has a well-recognized association with oesophageal adenocarcinoma, with phenotypic progression through dysplasia to malignancy. The nuclear phosphoprotein p53 is a putative tumour suppressor with mutations resulting in both loss of negative growth regulatory function and possible gain of oncogene function. Many mutant forms have a prolonged half-life and are demonstrable with immunohistochemical techniques. We examined 62 endoscopic oesophageal biopsies and 36 oesophageal resections for p53 overexpression using the monoclonal antibody DO-7 on paraffin-embedded tissue. The series included 40 cases of Barrett's metaplasia, 13 cases of dysplasia, and 81 cases of adenocarcinoma. None of the cases of metaplasia was p53-positive, compared with 4/13 cases of dysplasia and 52/81 cases of adenocarcinoma. There was no association between the degree of dysplasia and p53 expression, although a trend emerged of increasing p53 expression with higher tumour grade. We conclude that p53 overexpression is frequent in oesophageal adenocarcinoma and may be related to tumour grade. p53 overexpression is not restricted to neoplastic lesions and mutation of this tumour suppressor may occur early in the malignant progression of Barrett's oesophagus.

Adenocarcinoma arising in Barrett's oesophagus: evidence for the participation of p53 dysfunction in the dysplasia/carcinoma sequence

Adenocarcinoma arising in Barrett's oesophagus is often preceded by mucosal dysplasia, but little is currently known about the aetiology or natural history of this dysplasia/carcinoma sequence. To investigate the participation of the tumour suppressor gene p53 in this sequence, an immunohistochemical analysis of p53 protein overexpression, which is known to closely correlate with point mutation of the p53 gene, was conducted in 30 patients with Barrett's adenocarcinoma. Adjacent Barrett's mucosa was dysplastic in 21 (70%) patients. Sixteen (53%) tumours overexpressed p53, 10 of which had adjacent dysplastic Barrett's mucosa. In all 10 patients, this dysplastic mucosa also overexpressed p53, predominantly in areas of high grade compared with low grade dysplasia. In contrast, none of the dysplastic mucosa adjacent to 11 tumours lacking p53 overexpression showed detectable values of p53. These results suggest that p53 dysfunction may participate in the progression from dysplasia to carcinoma in some patients with Barrett's oesophagus.